1. Field
The embodiments described below relate generally to imaging, and may be applied to systems for generating in vivo images.
2. Description
Computed tomography (CT) systems are commonly used to generate images of an internal portion of a body. Generally, a CT system includes an X-ray source and a radiation receiver that are mounted to face one another on opposite sides of a ring. A body is positioned within the ring so that a portion of interest lies between the X-ray source and the radiation receiver. The X-ray source then emits X-ray radiation that passes through the portion of interest and is received by the radiation receiver.
The receiver produces a set of data that represent the attenuative properties of tissues that lie between the X-ray source and the receiver. This set of data comprises a projection image. The ring is then rotated in order to rotate the X-ray source and the radiation receiver around the portion of interest. During the rotation, the X-ray source transmits radiation toward the receiver and the receiver produces projection images corresponding to various rotational angle positions. A three-dimensional image may be generated from the projection images using known reconstruction techniques.
Most reconstruction techniques assume that the spatial distribution of the portion of interest's linear attenuation coefficient is identical for all projections. This assumption does not hold if the portion of interest is in motion during acquisition of the projection images. Therefore, in the case of periodic motion (e.g., resulting from breathing motion, heart beat, etc.), some reconstruction methods attempt to acquire projection images that each correspond to a same phase of the motion.
A common approach to acquire such projection images includes time-stamping the projection images during their acquisition and extracting subsets of the images such that each image in a subset corresponds to the same phase. The subsets are extracted by comparing the time-stamps of the images with an external temporal physiological or anatomical signal that is measured with an external device. An image may be reconstructed for a phase using the subset of projection images that corresponds to the phase. Moreover, images for several phases may be reconstructed and combined into an animated image showing movement of the portion of interest over several phases.
The above approach assumes that the temporal pattern of the signals is representative of the temporal pattern of the periodically moving anatomy. Accordingly, such approaches may not provide required accuracy. In addition, these approaches require additional devices for monitoring the physiological or anatomical signal, some discomfort due to the attachment of the monitoring devices to the patient, and/or additional time for patient setup.